It is always a good idea to register with the Embassy, even if you’ll only be in the country a short time. The State Department in Washington, D.C. receives calls every day asking, “Is my son/daughter/husband, etc. all right? I haven’t heard from them for a while.” These calls, called “welfare and whereabouts” cases, are forwarded to the respective Embassies, where consular officers are assigned to investigate. Their job is much easier if you have registered with the Embassy.
Call the Embassy and ask for the Consular Section. Tell them you want to register, and provide the information they ask for, which will be your full name and contact information. They’ll instruct you to inform them of any changes in that information. Do it. Your name will be on their calling list in the event of natural disasters or political upheaval. Tsunamis happen, as do revolutions, terrorist attacks in nightclubs, and more.
If you have gone far from home because you don’t want them to find you, you should still register with the Embassy, for safety’s sake.
This advice applies to non-American expats in the U.S. and elsewhere. Your Embassy wants to know how to reach you. For example, Mexico is trying to reach potential voters in the United States, and they’re havving a hard time doing it.